Co-axial plug and socket connectors comprise a co-axial plug and a co-axial bulkhead socket which, when plugged together and connected to one another, produce co-axial plug-in contact. To allow a plug and socket to be connected in the case of co-axial plug and socket connectors of the so-called N type, the socket has a thread on its outer circumference. The plug is fitted with a union nut which likewise has a thread, on its inner circumference. An N plug and an N socket are connected by being plugged together and a union nut of the N plug is screwed, by its inside thread, onto an outside thread on the N socket. The connection of co-axial plug and socket connectors of the N type in this way has long been known and provides a good and secure HF contact between the plug and socket. However, it is often felt to be a disadvantage that a screwing operation which takes a relatively large amount of manual effort and a relatively long time has to be performed to connect the plug and socket. In applications where, for example, a large number of co-axial connections have to be made between plugs and sockets, the manual effort and time spent adds up to a considerable total.